Herein, the dissolution behaviors of Al-Si casting alloy and cold rolled alloy anodes in AlCl3-NaCl-KCl molten salt were investigated at 423 K to produce high-purity Al from Al-Si alloys. All the Al-Si alloys were purified to more than 99.4 wt% by electrorefining. In particular, the purity of the AC4C and Al-11 %Si alloys was 99.9 wt% each. It was confirmed from linear sweep voltammetry (LSV) measurements that anodic dissolution did not occur in the Si molten salt electrolyte. The dissolution of Al occurred preferentially on the anode surface of the ADC12 alloy during electrolysis, while the undissolved Si formed an enriched layer on the surface. In the ADC12 and AC4C casting alloys, a microstructure identical to that of the bulk metal was observed on the surface after electrolysis. On the contrary, the Si microstructure in the cold-rolled Al-11 %Si alloy was fine, and adhesion was weak and did not remain firmly on the surface. In addition, the Si-enriched layer on its surface did not significantly affect the outcome of the 50-h electrorefining experiment.
Polymer electrolyte membrane (PEM) water electrolysis has received significant attention as a suitable technology for hydrogen production because it can operate at a high current density, is compact, and can produce high purity hydrogen. However, this process involves high costs because precious metal catalysts are required to maintain high performance. To overcome this challenge and develop new materials to replace precious metals, the complex overlapping overpotentials must be considered separately. In a previous study, a structure that uses double reference electrodes by shifting the electrode arrangement was proposed for separating the overpotentials. This structure allows the electrolyte surface potential to be measured by a reference electrode far from the electrode by changing the potential distribution. However, the structure may cause a complicated three-dimensional potential distribution, which may adversely affects accurate measurement of the electrode potential. Therefore, the potential distribution was analyzed and evaluated using three-dimensional multiphysics simulations incorporating proton and electron conduction. As a result, a remarkable phenomenon called potential wraparound, which affects the distribution of electric potential, was observed. Furthermore, a significant finding was that this effect can be suppressed by changing the shape of the electrode.
A stream of electron conductor powder (graphite, silver, and tin) was introduced to the measurement of Volta potential difference. The stream of the conductive powder was placed at the center of a vertical glass tube, while an aqueous electrolyte solution of KCl was run along the inner wall of the tube. The potential difference between the terminals of the streaming conductive powder electrode and the Ag/AgCl electrode inserted in the KCl solution was measured. From the experimental result, the real potential of the solvation of Cl− ion was determined. The values obtained by the present method were compared with the reported values based on the Kenrick method with mercury jet electrode.
A much higher cell voltage of ca. 2.5 V than that of the typical Li-S battery was successfully achieved by combining the 5 V-class, spinel-type LiNi0.5Mn1.5O4 (LNMO) as a cathode and the rubber-derived sulfur composite as an anode. The cycling performance of the cell was improved by the PVDF coating only the cathode and coating both the cathode and anode, in which the discharge capacity retention increased from ca. 45 % to ca. 60 %. On the other hand, there was no difference in the cycling performance between the cell with the PVDF coating only the anode and the cell without the PVDF coating both the cathode and anode. There was no difference between the cycling performance of the half-cell of the LNMO cathode with the PVDF coating and without the PVDF coating, indicating that the PVDF coating on the cathode side does not prevent degradation of the electrolyte solution on the cathode surface. These results suggest that the PVDF coatings of the cathode surface play an important role as a protective layer in preventing the direct contact and side reaction between the polysulfides and cathode surface, thus leading to improvement of the cycling performance.
Mixed anion oxyfluorides are one of promising candidates of fast fluoride-ion conductor for all-solid-state fluoride-ion batteries. In order to establish scientific guidelines for further development of oxyfluoride-based solid electrolyte, understanding the true impact of anion defect species on ionic conduction is important. In this work, Ruddlesden-Popper oxyfluoride Ba2ScO3F, which can accept relatively high concentration of various types of anion defects, is selected as a target material to reveal defect functionalities. Oxide-ion vacancy (VO‥), fluoride-ion vacancy (VF˙) and interstitial fluoride-ion (Fi') were introduced into Ba2ScO3F, and the influence of each anion defect on fluoride-ion conduction was investigated. The ionic conductivities in Ba2ScO3F were improved by introducing fluoride-ion defects (VF˙ or Fi'), while not improved by introducing VO‥. These suggest that the fluoride-ion migrates by interstitialcy diffusion through the rock-salt structure in Ruddlesden-Popper oxyfluorides, and tuning anion defects species can be rational and effective strategy for the development of fast fluoride-ion conductors based on mixed anion compounds.